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One pipe, pumped return system

TeePee Member Posts: 1
First question; is it ok to have half the system pumped and half not?
I've posted some system pics. One is above boiler piping. Does anyone see a problem here?
Another pic is an air handler ductwork with a steam coil for heat. The first floor radiators were removed and a/c and ductwork installed with heat coils. Question; is the piping correct and what is the flow check for?
Also, I don't have a pic but I'm wondering why there is an f&t trap so close to the condensate pump if there are f&t traps out in the system? Thanks for any help. I'm more of a hot water guy, but steam is just as exciting!


  • dopey27177
    dopey27177 Member Posts: 887
    Why is there a pump above the steam trap?

    Any 1 pipe steam system can have a condensate ump installed in it.
    There is the requirement. If there is not enough height from the discharge side of the stem trap for the condensate to re-enter the boiler by gravity you need a condensate tank and pump set to pump the condensate back into the boiler.

    Example: most one pipe steam systems operate at 1 1/2 PSIG. 1 1/2 psig will raise water in the water column 49 inches. This will prevent water from re-entering the boiler. The head pressure or pressure exerted by water in the water column must be at least 2 psig to reenter the boiler. This height is clled dimension B or in this case is 54".

    This is caused by the fact that the boiler pressure forces the water out of the boiler by the connection to the wet return.

    So the section of the system that has a stem trap on it must have a condensate tank and pump set on it. The condensate piping that does not require a steam trap can be piped directly into the boiler.

    JUGHNE Member Posts: 11,062
    I had a 2 pipe system with 2 zone valves. One zone was trying to use gravity feed into the discharge of the cond pump. The other zone used the pump as return.

    This system had the water hammer from hell. You could see 2" pipe move from it.

    After spinning my wheels a lot to fix things, (as this was put in by a large city boiler company...one assumes things were plumbed right by "pros".

    Talking with some older people about the building they said the boiler used to be another 1/2 level lower in an old building, this would change the water line drastically.

    I piped everything thru the cond pump and stopped most of the water hammer.
    (the dry return on gravity feed was not draining and the steam would meet that water.)

    No F&T was need in the boiler room. All the return lines were "dry", no steam, cond water only. All radiation had it's own traps, fan coils had F&T's, end of mains had F&T's. All of this stopped the steam at those traps and only water was headed to the cond pump.

    I added riser pipes to the top of the wet returns in order to see any steam that might be headed back. This would isolate the zone that had the bad traps, if any.

    I see a F&T at one of your zoned fan coils. It looks like it has to lift condensate about 6" to flow out the return pipe.

    That looks like a check valve on that supply to act as a vacuum breaker when the zone valve closes.